the question i can answer is about the horsepower to litres conversion--they are measurements of differant things, and there is a corolation (though not a direct one) between the two.

Litres is a measurement of cubic displacement--how 'big' the engine is--it is the same as a measurement of of cubic inches (e.g. 289, 318, 350, 460 etc.) it is a measurement of how much liquid it would take (theoretically) to fill all of the cylinders completely, if all of them were all the way open at once. these numbers can be converted directly.

be warned: we americans are an inexact lot, and so very often the numbers associated with the engine aren't the exact displacement. (e.g. the chevy 454 and the buick (?) 455 were built on the same block (same displacement) but were otherwise differant, hence slightly differant numbers to avoid confusion. (sort of)

Horsepower is a measure of how powerfull an engine is. i forget the exact formula but it has something to do with the ability to move a certain weight a certain distance in a certain amout of time. I am SURE someone out there will fill in this blank.

this is why the there is only a rough coorolation between h.p. and displacement. the size of the cylander is only one factor in how powerful an engine is.

for example, my mother--the geriatric speed-demon--just bought a new Honda S2000 roadster. her little blue car (stock) squeezes 240 horsepower out of a four cilynder engine with less than 2 litres of displacement (no typo: 240 from 1.99l in 4)

by comparison, that's more than twice the horse-power-per-cubic-inch of the hottest stock corvette 454's

Wellllll, I've looked up the horsepower article and reread Dave's message and have decided I'll wait until my son drives up from Chicago to give me an interpretation. I'm geriatric too, Dave, but am cautious about putting the pedal to the metal. This is one of those situations where you have to know a little before you can learn more. Meanwhile I'll keep looking at used pickups and fine tune my built in lie detector.

Torque is an instanteous measurement of twisting force. Torque is what accelerates your rig. It is measured in foot-pounds. One ft-lb is equal to a force of one pound on an arm one foot long. Or a force of a half a pound on an arm 2 feet long and so on.

horsepower = (torque X rpm)/5,252

torque = (horsepower X 5252)/rpm

hp = torque at 5,252 rpm

As previously discussd, one hp = 33,000 ft-lbs/minute

to get that in terms of rpm, we look at force of 1 pound on a 1 foot arm traveling one rotation. The circumference of a circle is 2 times pi or roughly 6.283, times the radius, which is our case is the 1 ft arm our 1 lb is applying force to around the circumference.

If we divide 33,000 by roughly 6.283, we get roughly 5,252 revolutions per 33,000 ft of circumference.

Why then, if torque accelerates, is horsepower important?

Because we can use gearing. If we have engine A that gets 80 ft-lbs at 2,000 rpm and run it through 1:1 gearing, we have 80 ft-lbs at 2,000 rpm. If we have engine B that only gets 40 ft-lbs at 4,000 rpm, we can run it through 2:1 gearing to reduce that speed to 2,000 rpm, and at the same time the gearing multiplies the torque by 2, so we wind up with the same output torque, 80 ft-lbs at 2,000 rpm.

The difference is in the weight of the drivetrain that has to be used. The high-torque/low-rpm engine requires a heavy duty drivertrain, where the low-torque/high-rpm engine transmits the power through speed and can use much lighter components.

That's why sports cars and bikes, are so quick, with so little torque. And frankly, the rest of the world has trucks with smaller engines turning higher rpms that often haul as much as our 500+ ft-lb monsters do. Sure the engine's screamin' at 100 km/h, but all that gearing hauls the load.

doew a bigger truck let you stop more quickly? please correct me, but it seems that if the trailer's brakes are in good shape, the opposite would be true. that is--if every wheel has an effective brake on it, isnt braking based on weight vs. square inches of rubber on the road?

A larger truck designed for a larger payload has larger brakes. As you note, the trailer brakes take care of it. However, if they ever fail, the truck picks up the whole load.

Keep in mind that a bumper pull trailer has a lot more mechanical advantage over the truck when trying to sway it, than a fifth wheel does. The weight and longer wheelbase of a larger truck gives the trailer a lot more to try to move.

Always should have better than average brakes but size of a vehicle at higher speeds will not slow you down faster - takes quite a bit of momentum to get a heavy truck up to speed with a tow - and conversely just as much to slow it down. The greatest advantage is that usually the bigger trucks come with heavier duty components and can more adequately control the trailer in adverse conditions if the driver is keen to vehicles handling characteristics with a load behind.

Where size matters the most - is whether the towing vehicle at least meets or excedes the rated weight of the trailer being pulled. If someone hooks up a 29 ft trailer to say a Grand Cherokee (like I once attempted) - the trailer WILL push the tow vehicle making at worst loss of control of both in any braking situation or at bare minimum - quite a few white knuckle experiences...

John, I have a Reese 10,000 lb. wt. distribution hitch that is rated for 1,000 lb. tongue wt. and spring bars rated at 1,000 lbs.
I definately use them on my 2500hd but they are connected to either the last link or next to the last link on the bar chains. You can tell that there is tension due to a slight bending of the bars. The ball platform is bolted into the lowest holes on the hitch mount but I would be happier if I had one more hole. I measured my ball heigth and on the last link of the springbar chain, I'm at 20" from the ground. One link tighter and I go to 21 1/2".

Jeanne,
I've always remembered torque by an easy definition, twisting power. A big block motor has had it's proponents for years due to the preponderence of torque available. One engine from the '60's and early '70's was the Chevy big block 396 cubic inch engine in SS396 Chevelles. This engine came in all types of horsepower ratings depending on year produced and the application. I remember a 375 horse version that really moved the SS396. You will hear the statement "There is no substitute for cubic inches" and when it comes to towing this is true. The old 283 and 327 cubic inch engines of the past from Chevy were good engines based on the small block "mouse" motor as is the 350 cu. in. or 5.7 litre engine. When it comes to the real low end grunt for larger trailers, the 454 cu. in. and 496 cu. in. (8.1) big block engines from Chevy as well as the old 460 cu. in. Ford engine are really good. Diesel engines offer even more torque than these gas engines therefore you see many towing larger trailers with Ford Power Stroke Diesel engines and the new Chevy Duramax which is a sweet engine. It takes years to understand all the cubic inch designations for all the engines out there and it can be quite confusing. Hope I haven't added to that.

Jeanarlene asked sometime ago about tire size and how it effects power and towing. In a nut shell, a larger tire will rotate (circumference) slower than the smaller stock tire there-by effectively reducing power to the ground. Changing to a lower gear with a larger tire will bring that tire back to factory specs at a given RPM and speed. I finally found my formulas so I could share with all.

an easier way to think of it is that the wheel is simply another "gear" in the system. think of riding a 10-speed bike, and how changing the drive gear (front, attached to the pedals) affects how easily or powerfully the back wheel is moved...along with the gear selected on the back wheel.

In first gear, its easy to pedal...you dont go very fast, but you can go straight up! same thing with a truck, the gear-ratios, and so forth.

Oscar, thanks for the formula. I will ponder it. Chuck, your analogy works too. I'm trying hard to sift through all these facts and be intelligent about choice of towing vehicle. My natural inclination however is to give first consideration to other aspects-- such as enough windows to ventilate Ginger-the- dog when she's sitting in the parked vehicle. A cheerful color that doesn't resemble a hearse. A power seat to shift arthritis around. I want enough torque (see, I'm learning) to drag Airabelle over the mountains but I want to do it in comfort. Bet there's a formula for that too.